Removal devices are commonly used in the medical field to remove unwanted components from a biological fluid. For example, in the field of blood processing and collection, it is common to remove leukocytes (white blood cells) from the biological fluid (e.g., blood) prior to transfusion of the collected blood or fluid to a patient, as leukocytes present in transfused blood can often cause adverse reactions in the patient receiving the collected blood or fluid. Typically, the removal device includes a filter medium that has pores sized and distributed to prevent the passage of leukocytes, thus providing a biological fluid that is substantially free of leukocytes.
The biological fluid enters the filter through an inlet port and flows through a filter medium. Typically, the filter medium (for leukoreduction) includes a plurality of sheets made of melt-blown, non-woven fibers which provide a network of pores and torturous path through which the biological fluid must pass. The filter (or other removal device) includes an outlet port on the opposite side of the medium through which the biological fluid exits the device. For effective and time-efficient filtration of the biological fluid, it is desirable that the fluid is well distributed across the membrane. Thus, efforts to provide filters that remove as many leukocytes as possible in a time-efficient manner and optimize the flow of the biological fluid in the removal medium are ongoing.